Filamentary cathode



J- HIRMANN 2,404,070

FILAMENTARY CATHODE Original Filed'Feb. 24,}943

I I'NVENTOR; Jiduw Human/z.

BY I

A TTORNEY Patented July 16, 1946 FILAMENTARY CATHODE Julius Hirmann, Hillside,

Corporation of America,

Ware

Original application Febru N. J., assignor to Radio a corporation of Delaary 24, 1943, Serial No.

476,906. Divided and this application December 5, 1944, Serial 3 Claims.

My invention relates to cathodes, particularly to cathodes of the filamentary type for use in radio tubes and the like.

This application is a division. of my U. S. Patent 2,370,538, February 27, 1945, for cathodes, application Serial No. 476,906, filed February 24, 1943.

Filaments of the type used in radio tubes and the like are lengths of fine wire welded at their ends to relatively heavy lead-in conductors. To prevent excessive breakage, it has been found necessary to aifix to the ends of each filament light metal tabs which in turn are attached by welding to the conductors. Because of the smallness and fragility of the filament wire, it is not practical to weld the wire to the side of a single rectangular piece of sheet metal. Apparently the welding heat necessary to weld a fine wire, such as tungsten, to a nickel tab embrittles the wire in the weld region so that a slight tension on the wire will break it.

The principal object of my invention is an improved tabbed filamentary cathode.

My improved filamentary cathode comprises a wire with two sheet metal pieces on opposit sides of the wire, the two pieces being welded together and to the wire. The weld region, however, terminates short of or inwardly from the edge of the metal pieces from which the wire xtends. The unwelded edge portion of the metal pieces flares outwardly and away from the wire so as to provide a slightly tapered funnel or ferrule for supporting the wire adjacent its point of attachment to the metal pieces. The method of making this cathode is disclosed in my U. S. Patent 2,380,525, July 31, 1945.

The characteristic features of my invention are defined in the appended claims and the preferred embodiment of my new tabbed cathode is described in the following specification and shown in the accompanying drawing in which:

Figures 1, 2, 3, 4, and 5 show, respectively, metal ribbon and wire during the successive steps involved in making my improved cathode, Figure 5 showing the finished tabbed cathode and two pieces of waste ribbon; and

Figure 6 is an enlarged longitudinal sectional view of the weld region of my novel tab and cathode.

Two metal ribbons, preferably of sheet nickel, and each of the type shown in Figure 1, are cut or blanked out to provide a plurality of uniformly spaced windows 3 between the edges of the ribbon. The two ribbons are then superimposed on on the other with the filament wire 4 between the two ribbons and substantially midway between the edges of the ribbons so that the wire extends lengthwise of the windows. The ribbons and the interposed wire are welded together in a weld indicated at 5, Figure 2, to secure the wire and the two ribbons together and make a cathode strip long enough to provide a large number of cathodes. While the filament wire is thus framed in the windows, the wire may, if an oxide coated cathode is desired, be coated with electron emissive material 6, such as barium and strontium carbonates. Thereafter the indi vidual cathodes are obtained by cutting the strip transversely along lines 1, preferably through the'weld 5 midway between the ends of the windows as shown in Figure 4, and then cutting away both side rails 8 of the window frame adjacent the weld region as shown in Figure 5, leaving the finished tabbed cathode of Figure 6.

A machine for performing the operations suggested in Figures 1 to 6 is shown by way of example in my U. S. Patent 2,370,538, February 27, 1945, of which this application is a division. Blanked out ribbons of the type shown in Figure 1 superimposed with the windows of the two ribbons in exact registry and the filament lying lengthwise of the ribbons in a position midway be tween the sides of the ribbons pass between welding electrodes, preferably of the roller type. The welding electrodes are so made and the Weld timing mechanism is so adjusted that welding starts and stops short of the ends of the windows shorter than the distance the ribbon at the ends of the windows. Since the wire is mechanically protected between the attached metal ribbons, it is conveniently handled and processed without danger of injury to the wire.

Good results have been obtained in sandwiching a tungsten-molybdenum filament wire .0005 inch (one-half of one thousandths of an inch) in diameter between two nickel ribbons, each .001 inch thick and .125 inch Wide with windows about .062 inch wide and .50 inch long, and with .250 inch spaces between the windows. Tabs .125 inch long and about .010 inch wide may be attached to both ends of the filament wire although the .0005 inch wire is so fine it may be broken with a strong draft of air.

One outstanding advantage of my new tabbed filament is that the Wire will not break at or near the weld region, even if the wire in the tab be somewhat ernbrittled by the weld heat. When wire of a metal as refractory as tungsten or tungsten-molybdenum alloy is pressed by welding electrodes against soft sheet metal, such as nickel, the welding current melts only the nickel, and the wire is pushed into the surface of the nickel. The embedded portion of the wire hence is sharply bent and strained and apparently contributes to the tendency of the Wire to break. However, when two pieces of nickel are pressed against opposite sides of the wire and welded, as taught by my invention, there is no tendency for the wire to bend near the nickel. Further, when the weld region terminates at a poilnt removed from the edges of the two nickel pieces, so that the weld region terminates short of or inward from the end edges of the windows, the unwelded edge portions of the nickel ribbon flare slightly to provide a funne1 or ferrule slightly tapered away from the wire. Hence, ductile wire unaffected by the weld heat extends into and between the two nickel pieces. No bending force can be applied to the wire at the weld region and the wire can be broken only by direct pull.

My novel tabbed filaments display no tendency to break at or near the tabs and no special care need be observed in welding the tabs to heavy wires or lead-in conductors.

I claim:

1. A tabbed filamentary cathode comprising aing inwardly from the edge of the sheet metal ieces from which the wire extends.

2. A tabbed filamentary cathode comprising a wire, two elongated sheet metal pieces parallel to and welded to opposite sides of the wire, the ends of the pieces being unwelded and flared slightly from the wire.

3. A filamentary cathode comprising a wire with electron emissive material on the wire intermediate the ends of the wire and a tab at each end of the wire comprising two sheet metal pieces on opposite sides of the wire with their edges toward the electron emissive material on the wire spaced a distance greater than the diameter of the wire, said sheet metal pieces and the interposed portion of the wire being welded together in a region spaced from said edges,

JULIUS HIRMANN. 

